A transparent conductive film refers to a thin film having high light transmittance and an electrically conductive property and has been widely used as a voltage apply type common electrode or pixel electrode of a liquid crystal display, an electrochromic display (ECD, an organic electroluminescence device, a solar cell, a plasma display panel, a flexible display, electronic paper, a touch panel, and the like.
As for transparent conducting oxides (TCOs), it is important to design a material which transmits light in the visible ray area and has high conductivity. In order to be transparent in the visible ray area (wavelength of 400 to 700 nm), an electronic energy band gap needs to be 3.1 eV or more equivalent to electromagnetic wave energy having a wavelength of 400 nm.
As representative oxide semiconductors satisfying such properties, there are ZnO (3.3 eV), In2O3 (3.7 eV), and SnO2 (3.6 eV). Typically, the TCO has light transmittance of 80% or more in the visible ray area and specific resistance of about 10−4 Ωcm or less as an electrical property.
In order to find a material used for such TCOs, there has been mainly conducted research in which various materials are doped or alloyed. In particular, In2O3 has the specific resistance lower than that of SnO2 or ZnO, and, thus, it was the first to be commercialized. ITO (Sn doped In2O3) has been used so far.
The ITO is a material having been used for an electrode for display in an LED, an LCD, a PDP, etc., a solar cell, and the like and has the low specific resistance of 10−4 Ωcm in general or 10−5 Ωcm in lab-scale which is close to specific resistance of metal.
However, the ITO has the disadvantage of high price since In is one of rare elements, and if it is exposed to hydrogen plasma often used in a flat panel display manufacturing process, In or Sn is reduced and electrical and optical properties may be deteriorated. Further, it is known that the ITO is an n-type semiconductor and cannot be converted into a p-type semiconductor. For this reason, it is impossible to constitute a homo junction circuit element with the ITO only.